1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method and an image forming program, and in particular to technology for suppressing unevenness in dot pitch.
2. Related Art
Some image forming apparatuses include a transfer belt as an image carrier and a cleaning brush as a cleaner, and clean a surface of the transfer belt with the cleaning brush. In other words, these image forming apparatuses have a cleaning brush that is in contact with a transfer belt. When forming an image by transferring a toner image applied to the transfer belt to a sheet-like material, some toner particles may remain on the surface of the transfer belt untransferred. The above image forming apparatuses electrostatically remove these remaining toner particles (i.e., residual untransferred toner particles) by rotating the cleaning brush while receiving a cleaning current (electric current for cleaning) at a predetermined current value.
The cleaning brush is made by, for example, weaving conductive fibers into a conductive base fabric, the conductive fibers being made from nylon fibers each having a diameter of 1 to 10 deniers, and so forth. As the cleaning brush is in contact with the transfer belt, part of the bristles of the cleaning brush bends (or, is in a bent state) from touching the transfer belt.
After this bent state lasts for a long period of time (e.g., after a long vacation and the like), forming an image with use of such a cleaning brush that partially remains in the bent state would give rise to the following problem: when the cleaning brush rotates, contact resistance between the bent part of the cleaning brush and the transfer belt becomes different from contact resistance between an unbent part of the cleaning brush and the transfer belt. This makes the rotation speed of the transfer belt irregular, and dot pitch accordingly becomes uneven.
There is a technology for suppressing such an unevenness in dot pitch caused by the partially bent state of the cleaning brush due to the lengthy cessation of the rotation thereof.
According to this technology, following such a lengthy cessation of the rotation of the cleaning brush, the cleaning brush is preliminarily rotated prior to the image formation so as to restore the bent part of the cleaning brush back to the unbent state (e.g., Japanese Laid-Open Application No. 2001-175139).
However, the problem with such a conventional technology is that after the lengthy cessation of the rotation of the cleaning brush, users cannot get the printer to start the image formation until the preliminary rotation is completed; this conventional technology thereby renders such an image forming apparatus user-unfriendly.
More specifically, when the cleaning brush is made of, for example, nylon fibers, it requires about 5 to 30 minutes of preliminary rotation to restore the bent part of the cleaning brush back to the unbent state. Since the users have to face the long waiting time, such an image forming apparatus is quite user-unfriendly, especially considering the fact that it only takes about a minute to warm up an image forming apparatus of recent years.